Offshore structures, such as oil and or gas platforms, are common. Oil and or gas platforms are designed to perform a variety of functions, such as drilling wells, extracting oil or natural gas and storing and performing preliminary processing on any oil or natural gas that is recovered. In order to perform these various processes, an offshore platform must be able to house all the necessary facilities to perform those processes. However, in view of the engineering challenges and cost associated with building a structure that can withstand the natural environmental conditions, such as forces imparted by sea waves, and accidents such as collisions with moving vessels, offshore structures are usually designed to be as compact as possible. As such, the structures are designed to make as efficient use of space as possible.
Nonetheless, it sometimes becomes necessary for an offshore structure to perform new functions, for example due to changes in technology or due to engineering challenges in extracting resources as they become depleted. In such cases it may become necessary to deploy new machinery and/or facilities on the existing structure. In some cases this is possible by replacing existing facilities. However, that is not always the case.
Therefore, it sometimes becomes necessary to provide more space on an offshore structure. One option is to create further decks or levels on the existing structure. Another option is to extend the platform sideways using cantilevered sections from the side of the existing structure. Another option is to create an entire new offshore structure in the vicinity of the first structure, and then to link the two structures together by a bridge, for example.
However, there are various disadvantages associated with the existing methods of extending offshore structures. Modifying an existing structure, by introducing new decks, strengthening existing decks, or adding cantilevered sections to the side of the structure can interfere with the ongoing functions of the offshore structure (such as drilling or extraction processes) requiring the structure to be taken offline while the upgrades are made. Further, such modifications can introduce increases in weight which must be borne by the existing structure, and this can be impractical in some circumstances. Creating a separate, second, structure, can also be impractical if the sea floor is already crowded with equipment and pipelines in the region of the first platform. Further, commissioning an entire new structure is expensive.
As an example of a previous method of extending an offshore structure, GB-B-1,525,242 discloses a conventional cantilever extension structure, supported by struts extending to the legs of the original structure, above the original foundation. As such the extension is supported by the legs, not the foundation. As another example, GB-A-2,203,782 discloses an extension structure built as a separate structure on a new foundation (different from the foundation of the original structure).
The present invention provides an alternative way of extending an existing offshore structure, and aims to at least partly solve some of the above-problems.